Computers are used all over the world to perform a wide variety of tasks. Computers perform these tasks by processing software code which contains commands that are interpreted and executed by the computer. Software code is typically written by a developer using one or more scripting or programming languages. Because most software programs are quite complex and involve the interaction of multiple functions, variables and processes, it is often necessary for the software code, or at least portions thereof, to be rewritten more than once. A typical development cycle may include many different versions which are tested, patched and then retested. Furthermore, once a software product has been released, functionality problems continue to be found and customers continue to demand new features. Thus, whether it is fixing a major security hole, a simple user-interface problem or adding new features, software updates and patches have become a common method for developers to deliver software changes to the program users.
Such continual updating and patching, however, can be an inconvenience for a home user, but is much more than an inconvenience for an IT professional at a large corporation responsible for hundreds or thousands of computers. Many times, software updates and patches may cause more problems than they fix. Thus, especially in a corporate environment, the patch should be tested before it is released to all of the computers in the network. In such cases, it is very advantageous for the computer user to test the patch on computer hardware identical (or very similar) to the other computers on which the patch will be installed. Testing, however, requires setup time, making a backup of the current system, reinitializing (sometimes rebooting), reconfiguring, etc. Because of this, many computer users, especially those responsible for large networks, typically have separate computers reserved for testing patches and updates.
One way to cut down on the time spent backing up and initializing a computer for testing is to use a virtual machine. A virtual machine may be thought of as a computer within a computer. The virtual machine (VM) is started in a software program running on the host operating system (using e.g. VMware™). The VM initializes (e.g., boots) as a normal computer, using virtualization technology to access the physical machine's hardware. Thus, if the same operating system (OS) and software applications are installed on the VM as are running on the host, the VM will have the same qualities and characteristics as the host machine.
In this environment, a patch can be tested on the VM without affecting the physical host machine. Furthermore, setup time can be greatly reduced by taking a virtual machine “snapshot”. A snapshot of a VM is basically an image of everything that is installed including operating system files, settings, drivers, data files, etc. Thus, the computer user can start up a VM, install an operating system and other programs such that the VM is identical to the host (physical machine), take a snapshot and begin testing. If the test fails, the IT professional can simply restart the VM using the snapshot from before the patch was installed and test the next patch. However, if the patch test was successful, the computer user must still reinstall the patch on the physical machine.